1. Field of Invention
The invention relates to an ink-jet head for printing by ejecting ink onto a record medium, and to an ink-jet printer having the ink-jet head.
2. Description of Related Art
In an ink-jet printer, an ink-jet head distributes ink, which is supplied from an ink tank, to pulse pressure chambers. The ink-jet head selectively applies pulse pressure to each pressure chamber to eject ink through a nozzle connected with each pressure chamber. As a means for selectively applying pulse pressure to the pressure chambers, an actuator unit or the like may be used in which ceramic piezoelectric sheets are laminated. The printing operations are carried out while reciprocating such a head at a high speed in the widthwise direction of the paper.
As for the arrangement of the pressure chambers in such an ink-jet head, there is a one-dimensional arrangement in which pressure chambers are arranged in, e.g., one or two rows along the length of the head, and a two-dimensional arrangement in which pressure chambers are arranged in a matrix along a surface of the head. To achieve high-resolution and high-speed printing, the two-dimensional arrangement of pressure chambers is more effective. As an example of ink-jet head in which pressure chambers are arranged in a matrix along a surface of the head, an ink-jet head is known in which a nozzle is disposed at the center of each pressure chamber in a view perpendicular to the head surface. In this case, when pulse pressure is applied to a pressure chamber, a pressure wave propagates in the pressure chamber perpendicularly to the head surface. Ink is then ejected through the corresponding nozzle disposed at the center of the pressure chamber in a view perpendicular to the head surface.
Here, in a case of ejecting ink by using a pressure wave, there is known a so-called “fill after fire” method, in which a positive pressure is applied to a pressure chamber, and a so-called “fill before fire” method, in which at first a negative pressure is applied to a pressure chamber and then, at a predetermined timing after a negative pressure wave has been reversed and reflected, a positive pressure is applied. In these two methods of “fill after fire” and the “fill before fire”, it is said that the “fill before fire” generally has a higher energy efficiency. Moreover, when a pressure wave propagates in a pressure chamber perpendicularly to the head surface, as in the aforementioned conventional example, the propagation time length of the pressure waves (i.e., AL: Acoustic Length) is extremely short, so long as a head is not large-sized. Furthermore, if the “fill before fire” is performed in the case of a short AL, the time period for the pressure waves to be reversed and returned becomes short, so that a time interval between timings for a negative pressure and for a positive pressure also becomes short. Because of this, a highly responsive and expensive drive circuit is necessary to be used in the ink-jet head. In addition, if the “fill after fire” is performed in order to avoid the above necessity, a large energy has to be inputted to the ink-jet head, so that the problem of a poor energy efficiency can be raised.